N/A
This invention relates to rechargeable cells with alkali or alkaline earth metal or metal-ion negative electrodes, particularly lithium or lithium-ion, and sulfur dioxide based electrolytes, and specifically to the design and methods of electrically operating such cells to improve the recycling life, reliability and electrical performance.
The improvement of lithium rechargeable batteries has been a topic of investigation since the early 1960""s. Even so, the attainment of 200 deep cycles was not possible until the 1980""s. The two primary problems were: (1) lithium dendrite formation which would puncture the separator, leading to short circuits and explosions; and (2) the operationally low cycling efficiency of the lithium electrode. Even if the lithium electrode cycling efficiency is 99%, the lithium electrode then loses 1% of its capacity each cycle. Thus, after 100 deep chargedischarge cycles, most of the lithium metal has reacted irreversibly with the electrolyte. The cell can no longer be cycled very deeply and has no value as a source of power for a consumer. Thus, it has always been standard practice for lithium metal electrode cells to be built with at least 100% and usually a 400% or more excess of lithium metal. A need exists for a rechargeable battery with the high specific energy and other desirable characteristics of alkali metal, alkaline earth metal or lithium-ion negative electrodes but without the disadvantages.
The present invention of a rechargeable cell with an alkali or alkaline earth metal, or metal-ion, negative electrode includes the physical design and materials used to construct the cell as well as the novel procedures devised to charge and discharge the cell during recycling. Such a rechargeable cell includes an alkali metal or alkaline earth metal electrode with a coulombic capacity about the same as the positive electrode of the cell, which may be a metal halide such as CuCl2, CuBr2 and the like, carbon or a metal oxide such as LiCoO2, MnO2 and the like, and a sulfur dioxide electrolyte solvent. The sulfur dioxide electrolyte contains a salt such as LiAlCl4 or LiGaCl4 that produces a halogen and/or a Lewis acid at the positive electrode on overcharge or at the negative electrode during overdischarge into reversal. On the majority of discharges the cell is discharged to a sufficiently low potential as close to 0.0V as practical without reversal for a sufficient time so that most of the alkali or alkaline earth metal including dendrites is either anodically dissolved or electrically isolated and scavenged. About every 4 to 50 cycles depending on the cycling conditions, the cell design and materials, the cell is overdischarged into reversal for a sufficient coulombic capacity to rebalance the state of charge of the positive and negative electrodes. Such rebalancing is necessary because the Li electrode becomes under charged during recycling. Overdischarge into reversal also generates halogen and/or a Lewis acid that reacts with and scavenges electrically isolated dendrites.